The recent growth in the market for displays has led to an increasing demand for higher definition images, and there is a need for optical materials that are not ordinary transparent materials but are optical materials having highly controlled optical properties.
Generally, a polymer exhibits birefringence because the refractive index of the polymer in a direction of its main molecular chain is different from the refractive index in a direction perpendicular thereto. In some applications, there is a need to control the birefringence precisely. Among components formed from macromolecular materials having the same total light transmittance, components formed from macromolecular materials having a smaller birefringence are required for protective films used for polarizing plates for liquid crystals. Triacetylcellulose is one of the representative materials used.
Under the foregoing circumstances, liquid crystal displays have increased in size in recent years, and this leads to an increase in size of their necessary components formed from macromolecular optical materials. In view of the above, there is a need for a material that exhibits only a small change in birefringence due to external force in order to reduce birefringence distribution caused by uneven external force.
Specifically, materials forming components that exhibit only a small change in birefringence due to external force are macromolecular optical materials that form components having a small photoelastic coefficient. Among such materials, acrylic-based resins are receiving attention as low-cost materials. One specific known material is a resin composition containing an acrylic-based resin and an aliphatic polyester-based resin serving as a plasticizer (see, for example, PTL 1). However, it has been difficult to obtain an optical film having a sufficiently small photoelastic coefficient even when the optical material disclosed in PTL 1 is used.